Lamp envelope with integral cooling chamber and method of making same



May 12, 1970 v. L. PLAGGE 3,

I LAMP ENVELOPE WITH INTEGRAL COOLING CHAMBER AND METHOD OF MAKING SAME Filed March 15, 1965 FIG.I.

FIG-3.

FIG.4.

INVENTOR Vernon L. Plogge AGENT United States Patent US. Cl. 220-2.1 Claims ABSTRACT OF THE DISCLOSURE A fluorescent lamp envelope of tubular open-ended configuration is provided with a depending tubulation which serves as a cooling chamber and mercury-vapor pressure control center in the finished lamp. The tubulation protrudes into a reentrant cavity formed in the bulb wall and is preferably recessed therein and, thus, within the envelope periphery to permit the envelope to roll freely during the various lamp-making and testing operations. A preselected part of the envelope side wall is first heat softened and displaced inwardly to form a reentrant cavity, and then a part of the deformed wall portion is reheated to the working point of the glass and shaped into an axially-extending recessed tubulation by a too] that is inserted into the open end of the envelope.

This invention relates in general to electric discharge devices and has particular reference to an envelope adapted for use in high-output type fluorescent lamps, and to a method for fabricating a mercury-vapor pressure regulating structure from a portion of the envelope wall.

As is well known, the mecury-vapor pressure within high-output fluorescent lamps must be maintained within prescribed limits if the lamp is to operate efficiently at its rated loading. Such control can be accomplished by providing a cool region within the lamp at which the excess mercury vapor will condense when the lamp is operated at the loading for which it is designed. As will be apparent, the difiiculty of maintaining such a cool region within the lamp increases as the lamp loading and bulb wall temperature increases.

Excellent control of the mercury-vapor pressure in such highly-loaded fluorescent lamps has been achieved by utilizing a tubulation which projects from an intermediate portion of the envelope and is recessed within a cavity or groove in the envelope wall. The temperature within the cooling chamber defined by the tubulation is maintained at the proper value by the current or air which passes through the groove around the tubulation and by the indented portion of the envelope wall which shields the tubulation from the heat radiated by the discharge. The aforesaid combination of a reentrant cavity and a recessed tubulation has provided satisfactory mercury-pressure vapor control in fluorescent lamps having power loadings as high as 50 watts per foot of lamp length. A high-output fluorescent lamp incorporating this type of cooling center or chamber is disclosed and claimed in copending application of Albert W. Wainio, Ser. No. 439,537 (now US. Pat. No. 3,331,977), which application is assigned to the assignee of the present application and is filed concurrently herewith.

The present invention is specifically directed to the problem of providing an inexpensive and convenient method of maufacturing envelopes for high-output fluorescent lamps of the type disclosed and claimed in the aforementioned copending Wainio application, and to the envelopes produced by such method considered as separate components or articles of manufacture. While the reentrant cavity could be molded into the envelope when the latter is being manufactured and a preformed tubulation subsequently sealed to the rim of an aperture provided in the shoulder of the cavity to provide an envelope having these features, the present invention avoids the costly and time-consuming operations inherent in this mode of manufacture by reshaping a preselected side wall portion of a conventional cylindrical envelope to form the cavity and then fabricating the tubulation from a part of the envelope wall itself. This is accomplished in a very inexpensive and simple manner by first heating a portion of the envelope wall to plasticity and displacing it inwardly to form the reentrant cavity, and then reheating a part of the deformed wall portion to the working point of the glass and shaping it into a tubulation by means of a tool that is inserted into the open end of the envelope. The resulting tubulation protrudes into and is preferably entirely recessed within the cavity so that the envelopes will roll-freely and the lamps can be fabricated, tested and packed in the conventional manner.

A better understanding of the invention will be obtained by referring to the accompanying drawing, wherein:

FIG. 1 is a side elevational view of a high output fluorescent lamp having an envelope made in accordance with the present invention;

FIGS. 2 and 3 are enlarged fragmentary views of the envelope illustrating various operations in the manufacture of the cooling chamber; and

FIG. 4 is a similar view illustrating the final step in constructing the tubulation embodiment shown in FIG. 1.

While the present invention may be employed in the manufacture of envelopes for various types of discharge devices that require a vapor-pressure regulating chamber, it is especially adapted for use in conjunction with highoutput fluorescent lamps and has accordingly been so illustrated and will be so described.

With specific reference now to the drawing, in FIG. 1 there is shown a high-output fluorescent lamp 10 which includes a vitreous light-transmitting envelope 12 made in accordance with this invention. The lamp is constructed in the manner disclosed in the aforesaid copending Wainio application and has a bipin base 14 attached to each of its sealed ends. These bases are connected toa pair of suitable electrodes (not shown) that are sealed within the envelope 12 in the usual manner. The inner surface of the envelope is coated with an ultraviolet responive phosphor and the envelope contains a measured amount of mercury and a suitable fill gas such as argon or neon, or a mixture thereof, at about 3 mm. pressure.

The vapor pressure of the mercury is maintained within the desired range of approximately 6 to 10 microns during lamp operation by means of a reentrant cavity, such as an arcuate groove 16, that extends across the surface of the envelope 12 in a direction transverse to the envelope axis; and by an elongated tubulation 18 that depends from an inwardly-sloped part of the envelope wall and is recessed within the groove. This tabulation is hermetically sealed at its tip and communicates with the interior of the envelope through an opening in the envelope wall. The groove 16 and tubulation 18 are so dimensioned and oriented that they provide a cooling chamber which effectively regulates the mercury vapor pressure during lamp operation in the manner disclosed in detail in the aforementioned copending Wainio application.

In accordance with the present invention, the groove 16 and recessed tubulation 18 are formed by modifying the configuration of a conventional straight cylindrical envelope and thus are defined by portions of the envelope wall itself. The method by which this is accomplished will now be described. The first step is shown in FIG. 2 and consists of heating a generally elliptical shaped portion A of the envelope wall to a sufliciently high temperature, as by a gas flame (not shown), to render it plastic. The heat-softened portion of the wall is then displaced inwardly toward the longitudinal axis of the envelope 12 to form the arcuate groove 16. As will be noted in FIG. 1, the arcuate opening defined by the displaced wall portion extends across the envelope in a direction transverse to the envelope axis. The groove 16 thus comprises a rounded depression similar to one which would be formed if a cylinder were pressed into and across the surface of the envelope at that point.

While the heat-softened wall portion A may be formed into the desired shape by means of a suitable mold or tool, a preferred and much cheaper technique is to hold the envelope in a generally horizontal position, heat an upwardly disposed portion thereof, and then let the softened glass sag into the desired shape.

The next step consists of heating a smaller and generally circular segment B of the deformed wall portion (see FIG. 2) to the working point of the glass so that it can be reshaped without puncturing the envelope wall. As will be noted in FIG. 2, the segment B is located near one end of the elliptical portion A and thus corresponds to an inwardly-sloped portion of the indented envelope wall.

After the wall segment B has been heated to the aforesaid temperature, a suitable tool such as a carbon rod 20, is inserted into the open end of the envelope 12 (see FIG. 3) and manipulated so that its tip engages the heated segment B, pushes it outwardly into the groove 16 and forms it into a generally cylindrical tubulation 1-8. The tool is then withdrawn and the glass is allowed to cool.

As will be noted in FIG. 3, the tip of the tubulation 18 is closed and is spaced from the bottom of the groove 16. The tubulation 18', by virtue of the manner in which it is formed, extends in the same direction and is generally parallel with the longitudinal axis of the envelope -12. It is also entirely recessed within the groove 16 and its diameter and length can be readily controlled by selecting a tool of the proper dimensions and shape. This completes the reshaping operation and the envelope can be phosphor coated, etc. and fabricated into a lamp in the usual manner.

However, if additional cooling of the tubulation is desired or required, the portion of the tubulation adjacent the envelope (the segment C in FIG. 4) is heated while the envelope is held in a generally horizontal position with the groove and tubulation facing downwardly. As the glass softens, the tubulation is allowed to sag a predetermined amount so that its tip lies just within the envelope preiphery, as indicated by the dotted line in FIG. 4. A tubulation 18 which is tilted or shifted away from the bottom of the groove is thus provided. Since the spacing between the tubulation and envelope has thus been increased, the tubulation will operate at a correspondingly lower temperature.

Reheating the tubulation in the aforesaid manner has another advantage in that the tubulation tends to collapse at the point which it is heated resulting in the formation of a neck or indent 22 which constricts the opening into the envelope as shown in FIG. 1, and more particularly in FIG. 4. This of course, decreases the amount of heat transferred by radiation and convection from the envelope proper into the cooling chamber.

Fluorescent lamp envelopes are generally manufactured from so-called soda-lime glass which is well known in the art. Glasses of this type have a softening point of about 696 C. and a working point of about 1010 C. Hence, unless a different type of glass is involved, the aforesaid groove-forming and tubulationforming operations are performed by heating the regions A and B of the envelope wall to (and preferably above) the aforementioned softening and working temperatures, respectively.

It will be appreciated from the foregoing that the objects of the present invention have been achieved in that a very convenient and inexpensive method of forming a recessed cooling chamber from a portion of the wall of a conventional cylindrical lamp envelope has been provided. In addition, an envelope adapted for use in a high-output fluorescent lamp has been provided wherein the vapor pressure control center is fabricated entirely from the envelope wall and is completely recessed within the envelope periphery. The envelope thus will roll freely and can be handled in the conventional manner during lamp manufacture.

While one embodiment has been illustrated and described, it will be understood that various structural and procedural modifications can be made without departing from the spirit and scope of the invention.

I claim as my invention:

1. A lamp envelope of vitreous material and elongated configuration having a deformed side wall portion that extends inwardly toward the envelope axis and defines (a) a reentrant cavity and (b) a depending tubulation that protrudes into said cavity, has an hermetically closed tip, and communicates with the interior of said envelope through an opening in said deformed wall portion.

2. The lamp envelope set forth in claim 1 wherein said depending tubulation is recessed within said cavity and the envelope periphery.

3. The lamp envelope set forth in claim 1 wherein said tubulation has a necked-in segment that constricts the opening into the interior of said envelope.

4. A fluorescent lamp envelope of vitreous material and open-ended tubular configuration having a deformed wall portion that defines (a) an arcuate reentrant groove and (b) a depending elongated tubulation that extends into said groove from an inwardly-sloped part of said deformed wall portion, has an hermetically closed tip, and communicates with the interior of said envelope though an opening in said deformed wall portion.

5. The fluorescent lamp envelope set forth in claim 4 wherein; said arcuate groove extends across the envelope in a direction transverse to the longitudinal axis of said envelope, and said elongated tubulation extends in the same general direction as the longitudinal axis of said envelope and is recessed within said groove and the envelope periphery.

6. The fluorescent lamp envelope set forth in claim 4 wherein said elongated tubulation is tilted toward the periphery of said envelope.

7. In the manufacture of an open-ended elongated glass envelope for a gaseous discharge device, the method of fabricating a vapor-pressure control structure from a portion of the envelope wall, which process comprises,

heating a preselected portion of the wall of said envelope until it becomes plastic,

displacing said heated wall portion inwardly toward the envelope axis and thereby forming a reentrant cavity in the envelope surface,

heating a part of said displaced wall portion to the working point of the glass, and then inserting a tool into said envelope through its open end and reshaping said heated part of the displaced wall portion by means of said tool into a tubulation that has a closed tip and extends into said cavity.

8. In the manufacture of an open-ended elongated glass envelope for a gaseous discharge lamp, the method of fabricating a vapor-pressure control structure from a portion of the envelope wall, which method comprises,

heating a preselected intermediate portion of the wall of said envelope to a temperature above the softening point of the glass,

displacing said heated wall portion inwardly toward the envelope axis and thereby forming an arcuate reentrant cavity in the envelope surface,

heating an inwardly-sloped part of said displaced wall portion to the working point of the glass, and then inserting a tool into said envelope through its open end and reshaping the said heated part of the displaced wall portion by means of said tool into an elongated tubulation that has a closed tip and extends laterally into and is recessed within said cavity. 9. In the manufacture of a cylindrical open-ended glass envelope for a fluorescent lamp, the method of fabricating a vapor-pressure control structure from a portion of the envelope Wall, which process comprises,

holding said envelope in a generally horizontal position, heating an upwardly-disposed portion of the envelope wall until it becomes plastic and sags inwardly toward the envelope axis and forms an arcuate groove that extends across the surface of the envelope, heating an inwardly-sloped part of the deformed wall portion to the working point of the glass, and then inserting a tool into said envelope through one end thereof and forming the heated part of said deformed wall portion by means of said tool into an elongated generally cylindrical closed tubulation that is recessed within said groove and extends in the same general direction as the envelope axis,

10. The method of fabricating a vapor pressure control structure from a portion of a cylindrical glass envelope as set forth in claim 9 wherein; said envelope is rotated after the tubulation is formed until the groove faces downwardly, and said tubulation is heated at a point adjacent the envelope wall to a temperature sufficient to partly collapse the tubulation and thus constrict the opening thereof into the envelope interior and also effect a predetermined gravitational displacement of said tubulation from its original position toward the periphery of the envelope.

References Cited UNITED STATES PATENTS 1,315,783 9/1919 Rossignol 65-108 1,970,223 8/1934 Case 313204 X ARTHUR D. KELLOGG, Primary Examiner US. Cl. X.'R. 

